An inkjet printhead is a device that discharges small droplets of ink at desired locations on a printing medium through nozzles, thereby forming a visible image of one or more color. Broadly speaking, an inkjet printhead may be classified into one of two types according to the mechanism employed for discharging the ink droplets. The first type is a thermal inkjet printhead that generates bubbles in ink using a heat source, and that discharges the ink droplets by the expansive force of the bubbles. The second type is a piezoelectric inkjet printhead, which uses a piezoelectric material to discharge the ink droplets by a pressure applied to ink due to transformation of the piezoelectric material.
With respect to the thermal type inkjet printhead, when a pulse type current flows through a heater formed, e.g., of a resistive heating element, the heat generated in the heater heats the ink adjacent to the heater almost instantly to about 300° C. As a result, the ink starts to boil, resulting the formation of ink bubbles that expand to apply a pressure to the ink filled in an ink chamber. The pressure causes the ink adjacent a nozzle to discharge from the ink chamber through the nozzle in the form of droplets. In a thermal inkjet printhead, it is generally understood that the nozzles have to be uniformly formed in order to achieve print quality.